There is a general need for materials with low dielectric constants (low-k) in the integrated circuit manufacturing industry. Using low-k materials as the interlayer dielectric (ILD) of conductive interconnects reduces the delay in signal propagation and signal crosstalk due to capacitive effects. The lower the dielectric constant of the dielectric, the lower the capacitance of the dielectric and the RC delay in the lines and signal crosstalk between electrical lines of the integrated circuit (IC). Further, the use of a low k material as an interlayer dielectric reduces the power consumption of complex integrated circuits.
Low dielectric constant (k) (“low-k”), insulators, with k significantly lower than that of SiO2 (3.9), are now used as inter-layer dielectric, e.g., as inter-metal dielectric (IMD) for reducing capacitive coupling and improving switching performance of integrated circuits (IC). For example, porous carbon doped silicon dioxide or fluorine doped silicon dioxide provide a dielectric constant of less than about 3.0. In this regard, the effective dielectric constant (keff) encountered by the signal in the interconnect structure is an important parameter.
Cu/IMD integration schemes typically involve the incorporation of other materials along with the bulk inter-metal dielectric material, forming a stack. These other materials may include copper diffusion barrier, copper capping layer and hardmask (e.g., CMP and etch stop) materials needed to prevent copper poisoning of the bulk low-k dielectric, to minimize electromigration, to protect the relatively soft low-k dielectric, and to facilitate the Damascene processing used in the device fabrication. These materials have a substantial impact on the effective k of the IMD stack. For example, an etch stop layer having a higher dielectric constant than the insulating IMD material located proximate to it increases the overall effective k of the IMD stack. Thus, materials used for etch stop, barrier and capping layers must meet the dual challenges of minimizing the effective k of the stack while providing material selectivity and protection for the IMD layers.
The challenges related to etch stop and barrier layer integration stem from the lack of low-k materials possessing suitable mechanical and electrical characteristics. While conventionally used silicon nitride (SiN) and silicon carbide (SiC) materials provide good etch selectivity and generally have good mechanical characteristics, their dielectric constant is very high. For example, SiN has a dielectric constant of about 7, and SiC formed using tetramethylsilane typically has a k value in the range of about 4.3-5.5. When used in a multi-layer stack with low-k IMD, such as carbon or fluorine doped silicon dioxide, having a dielectric constant of less than about 3.0, SiN and SiC raise the effective dielectric constant of the IMD stack to the levels that may not be acceptable for current and future levels of miniaturization.
There is currently a need in the IC fabrication industry for films with low effective dielectric constant that also possess properties that meet integration requirements developed for diffusion barrier films, etch stop films and the like.